The instant invention relates to an endless loop press belt construction, and further relates to a method of manufacturing the press belt.
Press belts are used in various press devices, such as shoe-type presses, as used in paper making machines and calendars, to transport a continuous fabric, web or sheet through a press nip.
The prior art press belts typically comprise a base weave which is covered on both sides and impregnated with a rubber or polyurethane material. The base weave acts as a reinforcing material to add strength to the belt. In this regard, U.S. Pat. Nos. 5,238,537 and 5,134,010 represent the closest prior art to the subject invention of which the applicant is aware. U.S. Pat. No. 5,238,537 describes a belt construction wherein the reinforcement material consists of a woven paper machine fabric which is impregnated from one side with polyurethane material. It has been found that this press belt is difficult to manufacture because it requires the woven reinforcing material to be dimensionally accurate so that the resulting belt is formed in exact dimensions. Furthermore, the resulting belt exhibits only limited elasticity. Accordingly, it does not readily withstand the flexing which occurs while running through the press. The belt is therefore subject to significant wear and must be replaced often. U.S. Pat. No. 5,134,010 discloses a press belt which is constructed on the outside of a casting cylinder. The press belt is formed by first laying a plurality of crosswise reinforcement yarns, under tension, at a distance from the outside of a casting form, and then helically winding a lengthwise reinforcement yarn around the crosswise yarns so as to provide reinforcement yarns running in both directions. Elastomeric material is then fed over the yarn layers and onto the outside of the casting form through a nozzle. Braces are used to support the crosswise yarns while the elastomeric material is fed by the nozzle. It can be seen that the crosswise yarns are situated adjacent the inner surface of the belt, and that the lengthwise yarns are situated adjacent the outside surface of the belt. While this particular method of manufacture is effective, it has been found that the method is unduly cumbersome because a complicated device is required to helically wind the lengthwise yarn on top of the crosswise yarns. In addition, a complicated nozzle construction is required, which makes the casting process difficult. Furthermore, it has been found that the resulting belt is not elastic enough to withstand the repeated flexing in the press because the outer layer of helically wound yarn causes the inner crosswise yarns to press together. The result is that the crosswise yarns resisting flexing as the belt moves through the sharp transition from the loop onto the concave surface of the press-shoe. Accordingly, the belt tends to wear very quickly and must be replaced often.
The instant invention provides a press belt consisting of separate layers of crosswise and lengthwise reinforcing yarns laid on top of each other and enclosed in elastomeric material. In contrast with the prior art, the crosswise yarns of the instant press belt are located adjacent to the outside surface of the press belt and the lengthwise yarns are located adjacent to the inside surface of the press belt. This arrangement of the yarns provides the proper tensile strength while retaining the elasticity required for use in shoe-type pressing devices. Since the crosswise yarns are adjacent to the outside surface of the belt, they do not tend to offer any resistance as the belt is run through the sharp transition curve from the belt loop to the concave press shoe. The instant press belt is formed by a method comprising the steps of laying the crosswise yarns inside the casting cylinder, casting a surface layer of elastomeric material over the crosswise yarns, laying the lengthwise yarns onto the still wet surface layer of elastomeric material and then casting an inner layer of elastomeric material over the lengthwise yarns wherein the inner and outer layers of elastomeric material form an integral elastomeric entity which encases both the crosswise and lengthwise yarns.
Accordingly, it is an object of the instant invention to provide a press belt which is rugged and durable while maintaining the flexibility for use in a shoe-type pressing device.
It is another object to provide a press belt having crosswise reinforcing yarns located adjacent to the outside surface of the belt and lengthwise reinforcing yarns located on adjacent to the inside surface of the belt.
It is yet another object to provide a method of manufacturing a flexible press belt which is simple and inexpensive.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.